Laser-induced fluorescence of nascent CH from ultraviolet photodissociation of HCCO and the absolute rate coefficient of the HCCO+O2 reaction over the range T=296–839 K

Abstract

The absolute rate coefficient of the gas-phase reaction HCCO+O2 was determined over the temperature range 296–839 K and at a pressure 7±1 Torr helium. The experiments were performed in a slow-flow kinetic apparatus employing pulsed photolysis of CH2CO at 193 nm as a source of HCCO radicals. Reaction time profiles of [HCCO] were constructed using a newly developed, sensitive spectroscopic technique in the visible spectral region to detect this radical: laser—induced fluorescence of nascent CH(X 2Π) photofragments following HCCO photodissociation at 266 nm. Photodissociation of HCCO at this wavelength was found to produce rotationally excited CH(X) populated to N″⩾26. The rate coefficient for the title reaction was found to be described by k(T)(HCCO+O2)=(2.6±0.3)×10−12 exp[−(325±80)K/T] cm3 s−1 molecule−1 (2σ errors). The absorption cross section of HCCO at 266 nm, σHCCO(266 nm), was also determined relative to that of CH2CO at 193 nm as σHCCO(266 nm)=0.07−0.05+0.20σCH2CO(193 nm).